1. Field of the Invention
The present invention relates to optical switching technology; more specifically, to a compact all optical switch utilizing mode conversion.
2. Description of the Prior Art
All optical switching is becoming a critical necessity for modem telecommunications based on optics. In order to accommodate the huge signal capacity made possible with optical signal transmission, the optical switch fabric needs to have a large range of input ports, from 2 to 50,000, in which each port can be switched to any of 2 to 50,000 outputs without interfering with other signals. Permitting multiple signals to be switched without interfering with other signals is referred to as a non-blocking arrangement. For this non-blocking function to be realized, the switch is usually dilated-which is accomplished by there always being, for each switch signal, a path within the switch that is separate from other signal paths. A dilated switch can necessitate a total switch size that is so large that it is substantially impossible to fabricate on typical integrated optics wafers or via bulk optics. The switch is described as "dilated" because the path separation requirement results in the maximum total number of waveguide paths in the cross section of the switch, at the midpoint of the switch, to be 2.sup.2N between which the paths must be connected where N is the total number of waveguide paths. Since these paths can be displaced from each other by 2.sup.2N (waveguide spacing), large directional changes in the waveguide from the straight paths must be accommodated in the planar surface. This consumes a large amount of valuable wafer space. Thus, for a 2.sup.2N .times.2.sup.2N switch, a total of 2.sup.N+1 (.SIGMA..sub.N=1 2.sup.N) {=2.sup.N+1 (2.sup.N -1)} "1.times.2" switches are needed. For example, a 256.times.256 switch requires 130,560 "1.times.2" switches. At present, a typical switch cost for a "1.times.2" switch is hundreds of dollars, so a 256.times.256 switch could cost more than several million dollars. Furthermore, the cost of a non-blocking switch increases as the square of the number of input ports which would make a 50,000 port device approximately 40,000 times as expensive as the 256.times.256 switch. Even allowing for a very optimistic projection of cost reductions so that the per port cost decreases by a factor of 100, to a few dollars per switch, the switch components alone would prohibit the development of such a device with an intrinsic cost in the billions. Undoubtedly integrated optics fabrication will eventually greatly reduce the per port costs for switches, but the need for a dilated switch design inherently limits the size of such devices. This limitation is not due to the size of the switch elements, but the size of the cross connect region between switch halves which has to be large to allow low loss transitions between all ports. Depending on the switch size, typical wafers of 5 to 6 inch diameters are generally limited to 16.times.16 devices and cost several thousand dollars per port. Thus, this solution is no different than present bulk optic solutions and nowhere near the few dollars per "1.times.2" switch cost described in the foregoing.